1. Field of the Invention
The present invention relates to a heat-shrinkable resin tube for forming a resin layer on a rotary member for an image forming part, a rotary member for support, a rotary member for paper discharge, and the like in an image forming apparatus such as a copy machine, a printer, or a facsimile, and to a rotary member for an image forming apparatus, the rotary member including the resin tube.
2. Description of the Related Art
In image forming apparatuses, various rotary members for an image forming part, such as a developing roller, a charging roller, and a transfer roller, are used in the electrostatic process. In such a rotary member for an image forming part, a resin layer is formed using a heat-shrinkable resin tube in order to ensure durability, wear resistance, a toner releasing property, etc. Japanese Unexamined Patent Application Publication No. 2003-211542 describes that a charging roller, a transfer roller, or a developing roller is covered with a heat-shrinkable, conductive, aromatic polyester tube.
Heat shrinkability is imparted to such a resin tube by stretching the tube at least in the radial direction. An example of a method for stretching a tube includes continuously supplying an unstretched tube in a stretching pipe, applying an internal pressure to the tube to inflate the tube, and bringing the inflated tube into contact with the inner wall of the stretching pipe to control the inflated diameter of the tube.
Heat-shrinkable resin tubes in the related art have, on the inner and outer surfaces thereof, scratches and traces of rubbing formed by being rubbed with a fixing member such as a stretching pipe or a guide plate during the manufacturing of the resin tubes. Such scratches including traces of rubbing may cause cracking and splitting of the tubes. In particular, in the case where the wall thickness of a tube is small, the tube is easily broken by the scratches, and thus it is difficult to manufacture such a tube. Furthermore, even if such scratches become substantially invisible after thermal shrinkage or baking of the tube, the scratches may cause cracking and splitting, for example, during covering of a rotary member with the tube or during practical use of the rotary member. When the rotary member for image formation, the rotary member being covered with the tube, is used, the cracking and splitting may become a cause of defects of an image formed by the rotary member. In addition, such cracking and splitting cause a problem in manufacturing various rotary members in an image forming apparatus, such as a rotary member for image formation.